Rosin is a solid resinous material that occurs naturally in pine trees. There are three major sources of rosin, (1) gum rosin is from the oleoresin extrudate of the living pine tree, (2) wood rosin from the oleoresin contained in the aged stumps; and (3) tall oil rosin from the waste liquor recovered as a by-product in the Kraft paper industry.
Rosin or colophony is the residue left after removing the volatile oils from crude oil of turpentine by steam distillation. It is composed mainly of abietic acid which is a very brittle solid that breaks with a glassy fracture.
The aged virgin pine stump is the source of wood rosin. The stump is allowed to remain in the ground for about ten years so that its bark and sapwood may decay and slough off to leave the heartwood rich in resin. Hercules Inc., of Wilmington, Del., has found that production of pine stump wood rosin can be artifically stimulated by injecting the herbicide, paraquat, into the lower portion of a living tree. This treatment of the stump produces Pinex.TM. rosin. The conversion of Pinex.TM. and also tall oil rosin into replacements for petroleum based extender oils is a portion of the instant invention.
Rosins derived from both oleorosin and aged stump wood are composed of approximately 90 percent resin acids and 10 percent nonacidic components. Rosin acids are monocarboxylic acids having the typical molecular formula, C.sub.20 H.sub.30 O.sub.2. Over the years, nomenclature of individual acids has changed. In addition to trivial names, such as abietic, levopimaric, etc. three different numbering systems have been used. IUPAC nomenclature names rosin acids as derivatives of abietane. The following is a structural formula for abietic acid: ##STR1## wherein the spacial relationship of substituents on asymmetric carbon atoms are designated as .alpha. or .beta. to denote whether the substituents are above or below the plane of the paper. For example, .alpha.-methyl denotes the methyl group as below the plane and is represented by a dotted line, while .beta.-methyl would be above the plane and is represented by a solid line.
Rosin acids combine to form resin acids which are characterized by high molecular weight, usually a variation in the weights of the rosin acid molecules which comprise it, and a gummy or tacky consistency at certain temperatures. The resins described herein are not the synthetic resins known to the art of polymer chemistry.
The resin acid molecule possesses two chemically reactive centers, the double bonds and the carboxyl group. Through these, many modifications in structure and numerous derivatives are obtainable. Because resin is composed of a number of rosin acids, the chemistry of its reactions is relatively complex.
In addition to the double bond reactions, rosin acids also undergo typical carboxyl group reactions. Salts and esters of rosin are important commercial derivatives of rosin. Other reactions involve the reduction of the carboxyl group to the alcohol and the conversion of the carboxyl group to the nitrile.
The structurally hindered nature of the rosin acid carboxyl group makes it necessary to use high temperatures or generally drastic conditions to bring about decarboxylation and usually, complete aromatization, which unfortunately produces highmelting white solids.
Various types of rosin acids have been used as extenders for high molecular weight SBR. Properties of GR-S Extended With Rosin Type Acids, L. H. Howland, J. A. Reynolds, and R. L. Provost, Industrial and Engineering Chemistry, Vol. 45, No. 5, May 1953. Also included in these initial studies were several nonrosin acids which included tallow fatty acid, oleic acid and naphthenic acid. Reasonably good cured physical properties can be obtained with the rosin type acids, whereas relatively poor physical properties are obtained with the nonrosin acids. Problems associated with the use of rosin acids are cure retardation, high tack and poor low temperature performance, which limit their use as an extender in rubber formulations.
U.S. Pat. No. 3,985,701 discloses an oil-containing rubber prepared by mixing a rubber selected from the group consisting of natural rubber, homopolymers of conjugated diolefins and copolymers of conjugated diolefins with ethylenically unsaturated monomers, with mineral oil having at least a 10 weight percent aromatic compound conten which is obtained through a specific chemical process.
U.S. Pat. No. 4,324,710 discloses the use of naturally occurring thermoplastic resins as substitutes for process oils. The resins are derived from crude wood rosin which have an acid number between 40 and 105.
U.S. Pat. No. 1,852,244 discloses a method of producing rosin oil (thermal oil) which consists of heating the rosin acids in the presence of a fuller's earth catalyst.
The use of heat as the sole means to decarboxylate wood rosins is very inefficient and energy intensive. The introduction of catalysts in the production of rosin oil or thermal oil has led to many improvements both with respect to reduced reaction time and improved quality. Known processes to decarboxylated wood rosins, such as U.S. Pat. No. 1,852,244, have the problem of catalyst residue in the thermal oil or rosin oil. When the thermal oil is intended for use in rubber, even minute amounts of foreign materials, such as catalyst residues, will have a deleterious effect on final product properties.
Rosin oils or thermal oils have been produced by decomposing rosin acids at high temperatures, and it has been known to produce a neutral rosin oil by the treatment of rosin with heat and hydriodic acid or iron turnings. In addition, the oil is sometimes distilled over alkali in order to free it entirely from rosin acids.
According to the concepts of the present invention, it has been unexpectedly found that naturally occurring rosin or resin acids can be economically and efficiently, partially or totally decarboxylated to yield a material that is suitable for use in rubber formulations. The prior art does not suggest or disclose the use of decarboxylation accelerators such as high sulfur content tall oil, Vinsol.TM. resin, fatty acids, organic sulfides and inorganic sulfides.